Apparatus for detecting rate of change of speed



3mm 15, 1943. cANETTA g- 2,321,992

APPARATUS FOR DETECTING RATE 0F CHANGE OF SPEED Original Filed Aug. 15,1940 2 Sheets-Sheet 1 INSULATION 2 mvEN'ro s JOHNOAN TTA PAUL. N.BOSSART av J 1943 J. CANETTA arm.

APPARATUS FOR DETECTING RATE OF CHANGE OF SPEED 2 Sheets-Sheet 2Qriginal F119?! Mg. 15, 1940 P UL N. OSSART BY v ATTORNEY and slides.

Patented June 15,1943 I APPARATUS FOR DETECTING RATE OF CHANGE OF SPEEDn. Canetta, Wiikinsburg, and Paul N. Bossart, Cheswick, Pa., assignorsto The Westinghouse Air Brake Company, Wilmerding, poration ofPennsylvania Pa., a cor- Original application August 15, 1940, SerialNo.

352,770. Divided and, this application January 30, 1941, SerialNo.376,599

9 Claims.

This invention relates to apparatus for detecting rate of change ofspeed of an element and particularly the rate of change of rotationalspeed of a rotary element, this application being a division of ourprior application, now Patent 2,270,414.

Our present invention is adapted to detect a rate of change of sp ed. ofa rotary element in excess of a certain rate and operate for a desiredpurpose such as alteration of the rotative condi-tlon of the rotaryelement. Various uses of our invention will occur to those skilled inthe art but for illustrative purposesour invention-is shown anddescribed in connection with a fluid pressure brake equipment forrailway cars and trains in order to release the brakes on a slippingwheel to prevent sliding of the wheel.

As is well known, if the degree of application of the brakes associatedwith a vehicle wheel becomes suflicient to exceed the limit of adheslonor rolling friction betweenthe wheel and the rail or road surface onwhich it rolls, the wheel decelerates promptly, at an abnormally rapidrate to a locked or non-rotative condition Sliding of railway car wheelsis ob- Jectionable because it develops flat spots on the wheels,thereby-necessitating replacement or re- Pair of the wheels.

In the subsequent description of our invention, the term slide refersonly to the dragging of a wheel along the rail or road surface in alocked condition. The rotation of a vehicle wheel at a speed less than aspeed corresponding to vehicle speed at a given instant is referred toas slip. or, a slipping condition." The distinction between the termsslide and slip should accordingly be home in mind.

Under the most favorable conditions of adhes on or rolling frictionbetween a wheel and the rail on which it rolls, a certain maximum rateof rotative decelerationof the wheel due to braking is possible withoutcausing the wheels to slip.

.to rotatively decelerate at a slipping rate. This the degree ofapplication of the brakes associated with a slipping wheel causes thewheel to cease decelerating and begin to accelerate back toward a speedcorresponding to vehicle speed, without actually decelerating to alocked or nonrotative condition and sliding.

Up to the present time, the proposeddevices which are responsive to therate of rotative de- Moreover, such devices have been associated di-vrectly with the vehicle wheel or the axle connecting a pair of wheels,as by mounting the devices in a separable casing attached to the journalat one end of a wheel axle in place of the usual end cover and in suchmanner that the rotary element of the devices are in coaxial cou pledrelation toone end of the wheel axle.

Due to the inherent weight of such devices and the fact that they aresubject to the constant shock and vibration due to. travel of thevehicle along the rail, the friction and wear on the bearings of therotatable elements of the devices has been found to be excessively high.Such friction may, if permitted to continue lon enough, interfere withthe accuracy and sensitivity of the devices to the rate of change ofspeed of the vehicle wheel and will in any case necessitate undesirablyfrequent servicing or repair. I

It is an object of our invention, therefore, to provide a novel type ofapparatus for detectin or registering the rate of change of rotationalspeed of a rotary element, such as a vehicle wheel, which inherentlyavoids the difliculties presented by prior devices.

Incarrying out the above object, we have utilized apparatus similar insome respects to the apparatus disclosed in the copending application,now Patent 2,270,413, of John Canetta, one of the present jointapplicants, which patent is assigned to the same assignee as the presentapplication. In this patent a commutator device is provided which isrotatable according to the rotational speed of a wheel of a vehicle foralternately charging a condenser to the voltage of a substantiallyconstant voltage source and discharging the condenser into a dischargecircuit automatic and instantaneous rapid reduction in repeatedly inrapid succession so as to produce a pulsating direct-current in thedischarge circuit substantially proportional to the rotational speed ofthe wheel. Our present invention so modifies the discharge circuit ofthe apparatus shown in Patent 2,270,413 as to cause pick-up of a elaytherein only in response to deceleration of the vehicle wheels at a rateexceeding a certain rate occurring, for example, when the wheel slips.

It is another object of our invention to provide apparatus'of thecharacter indicated above and further characterized by an arrangementadapted to cause operative response of the relay in the dischargecircuit whenever the rotary element rotatively decelerate at a. rateexceeding a certain substantially uniform rate notwithstanding variationin the rotational speed of the rotary element over a wide range.

It is another object of our invention to provide apparatus the typeindicated in the foregoing objects and further characterized by anarrangement for compensatingior the number of.

rotary elements employed in a system.

The above objects, and other objects of our invention which will be madeapparent hereinafter, are attained by several embodiments of ourinvention subsequently to be described and shown in the accompanyingdrawings wherein,

Fig. 1 is a diagrammatic view illustrating the principal object of ourinvention as applied to two separate wheel units ofwa car, as forexample the two wheel units of a four-wheel truck,

Fig. 2 is an enlarged fragmental view partly in section, showing detailsof construction of the commutator devices associated with the individualwheel units shown in Fig. 1,

Fig. 3 is a diagrammatic view, showing a development of the commutatordevice in Fig. 2 and illustrating the relative positions of the brushesassociated with the commutator device.

Fig. 4 is a fragmental diagrammatic view, showing a modification oi theapparatus in Fig. 1, and

Fig. 5 is a diagrammatic view, showing another modification of theapparatus in Fig. 1, and adapted for operation in connection with asingle railway car or a train of cars.

Description of equipment shown in Fig. 1

Referring to Fig. 1, the equipment shown is illustrated as applied to afour-wheel truck having a pair of wheel units l I and I, each unitcomprising two wheels, only one of which is shown, connected by andfixed at opposite ends to an axle i2 in well-known manner. Forconvenience and simplicity, details of the truck structure are omitted.Similarly, the brake shoes associated with the wheels and the brakeoperating lever mechanism or brake rigging therefor have been omitted,it being understood that the brakes may be of the conventional claspshoe type applied by supplying fluid under pressure to brake cylinders I3 and released by releasing fluid under pressure therefrom.

The supply of fluid under pressure to the brake cylinders i3 and therelease of fluid under pressure therefrom may be eifeoted under thecontrol of the operator of the vehicle by any suitable and well-knowntype of fluid pressure brake control apparatus. For simplicity, theoperatorcontrolled apparatus is illustrated as comprising a train pipel5, hereinafter called the control pipe, which may extend from car tocar throughout a train, the sections on successive cars being connectedby suitable hose couplers (not shown) in conventional manner; areservoir l6, herein-'- after referred to as the main reservoir, whichis maintained charged at a suitable fluid pres sure, such as one hundredpounds per square inch, from a suitable fluid compressor not shown: anda manually operatedbrake valve i! of well-known self-lapping type forcontrolling the fluid pressure in the control pipe IS.

The pressure chamber at one side of the usual piston in each brakecylinder I 8 is connected to the control pipe l5 by a correspondingbranch pipe i8 so that the fluid pressure in the brake cylinder i8normally corresponds .to the fluid pressure established in the controlpipe IS.

The brake valve I1 has an operating handle IIa which is effective in itsnormal brake release position through the medium of a rotary operatingshaft to condition the self-lapping mechanism of the brake valve I! toexhaust fluid under pressure from the control pipe l5 through an exhaustport and pipe iii to establish atmospheric pressure in the control pipeand correspondingly in the brake cylinders Hi. When the brake valvehandle "a is shifted in a horizontal plane out of its normal releaseposition into a so-called "application zone, the self-lapping mechanismof the brake valve is operated to cause fluid under pressure to besupplied from the main reservoir l6 to the control pipe IS, the fluidpressure established in the control pipe corresponding substantially tothe degree of displacement of the brake valve handle I la out of itsbrake release position. Thus, by shifting the brake valve handle 11a todifferent positions in the application zone having different degrees ofdisplacement with respect to the release position thereof, the pressurein the control pipe l5 and in the brake cylinders l3 may becorrespondingly controlled by the operator.

If the pressure in the control pipe I6 is reduced due to leakage orother causes referred to hereinafter, the self-lapping mechanism of thebrake valve automatically operates to supply fluid under pressure to thecontrol pipe to maintain a pressure therein corresponding to theposition of the brake valve handle. This pressure maintaining featureshould be home in mind in connection with the subsequent description ofthe operation of the equipment.

According to our invention, there is interposed in the branch pipe I 8leading to the brake cylinder l3 for each wheel unit a double-beatmagnet valve of suitable type which is controlled by a correspondingelectrical apparatus 22 responsive to the rotative deceleration of thecorresponding wheel unit at a slipping rate so as to release fluid underpressure from the associated brake cylinder l3 independently of theoperatorcontrolled apparatus.

The electrical apparatus 22 comprises a commutator device 23 secured tothe end of the wheel axle i2 of each wheel unit in the manner shown inFig. 2; an electrical condenser 24; a source of direct-current voltage,such as a storage battery 25; three contact fingers or brushes 26, 21and 28; a condenser unit 29; a relay 3| of the polarized type; and anon-inductive resistor 32.

As will be apparent in Fig. 2, the commutator device 23 may comprise abase member 36, in the form of a solid cylinder of insulating materialwith a flange 31 at one end secured as by a plurality of screws 38 tothe end of the axle 12 of a wheel unit in coaxial relation to the axleand rotatable therewith. The commutator device further comprises a ring39 of suitable metal, such as copper, brass or alloys thereof, which isembedded in the outer end surface of the insulating base 35 or otherwisesuitably afllxed thereto. The ring 39 comprises a continuous portionhaving a plurality, illustratively shown as eight, contact fingers ll.The fingers 4| are of uniform width and spaced equal distances apart.The outer surface of the fingers 4| is flush with the outer surface ofthe intervening surface of the insulating base 86.

The brushes 26, 21 and 28may be carried by suitable brush holder inconventional manner, not shown, which is in turn supported from orsecured to the inside of the axle journal. As indicated in Figs. 2 and3, the brushes 2'! and 28 are located in the same transverse plane inalignment with each other so as to engage the fingers 4! of the ring 39whereas the brush 26 engages the continuous portion of the ring 39. Forillustratlve purposes, the brushes 21 and 28 are separated by an angleof approximately 157 although, as will hereinafter appear, any othersuitable angular relation thereof for effecting the same result may beemployed, The brush 26 is indicated as having a certain angular relationto the brushes 21 and 28 but, as will be apparent from subsequentdescription the angular position of this brush relative to brushes 21and 28 is immaterial.

As indicated in Fig. 3, the angular spacing-between the two brushes 21and 28 is-such that these brushes are alternately engaged by the contactfingers 4! of the ring- 89 of the commutator device, as the base 86 isrotated on its axis. Thus,

' when the brush 28 engages a contact finger 4|, as

shown, the brush 2? is not engaged by a contact finger, and vice versa.

It will thus be understood that the commutator device 23 is effective,upon rotation, to alternately connect the brush 26 to the brushes 2'!and 28.

As will be seen in Fig. l, the brush 2! is connected by a wire 25 to oneterminal of the battery 25, hereinafter taken to be the positiveterminal, and that the brush 26 is connected to the opposite or negativeterminal of the battery 26 by a wire 46 in which is interposed thecondenser 24. The negative terminal of the battery 25 isgrounded as at41. Thus, when the commutator device 23 connects the brushes 26 and 21,a circuit is established for charging the condenser 24 to the voltage ofthe battery 25.

Connected between the brush 28 and ground at a point 48, is a circuitincluding two parallel branches, one of which includes the resistor 32and the other of which includes the condenser unit 29 and the polarizedrelay 3| in series relation. Accordingly, when the commutator device 23connects the brushes 26 and 28, the electrical charge stored in thecondenser 24 is discharged through the resistor in the dischargecircuit.

As in the copending sole application, Serial No. 342,935 of John Canettamentioned above, the condenser 24 and its charging circuit are sodesigned as' to have a charging-time constant that is small relative tothe time of charging or the time that the charging circuit is closed.Accordingly, each time the charging circuit is espressed across thecondenser. This may be expressed in the form of the following equation:

(1) Q=CE condenser 24 were completely discharged thenv the alternatechargingand discharging of the condenser repeatedly in rapid successionwould produce a pulsating direct-current in the discharge circuit whichwould be directly proportional to the frequency or number of times persecond that the discharge circuit is established.

As is well known, the unit of electrical current. the ampere, is theequivalent of a coulomb of electricity per second. Thus, the current inthe discharge circuit in amperes would be theoretically equal to thequantity Q, in coulombs, discharged from the condenser 24 each time thedischarge circuit ls established multiplied by the frequency f or thenumber of times the discharge circuit is established per second. Thisrelation may be expressed mathematically by the equation:

It will be readily apparent from Equation 2 that assumingq' to be aconstant, the current I in the discharge circuit varies in directproportion to the frequency 1.

Obviously. the frequency of establishment of the discharge circuitdepends not only upon the number of revolutions per second of thecommutator device 23 but also on the number of contact fingers 4|, whichmake and break the discharge circuit a corresponding number of timesduring each revolution. Thus the frequency may have any desired range byselecting a desired number of contact fingers 4| for the commutatordevice In actuality, the same quantity of electricity is not dischargedfrom condenser 24 each time the discharge circuit therefor isestablished because of the variation in the voltage-drop across theresistor 82 with variation in the rotational speed of the commutatordevice 23. This will be apparent when, by analogy to Equation 1, it isunderstood that the quantity of electricity discharged from a condenseris equal to the capacitance of the condenser multiplied by the change inthe voltage impressed on the condenser. Assuming that Q is the quantityof electricity in coulombs discharged from a condenser, C is thecapacitance tablished, the same quantity of electricity is tricity sostored in condenser 24 will be a constant because the quantity Q ofelectricity, in coulombs, stored in a condenser is equal to the productof the capacitance C, which is a constant, of the condenser in faradsand the voltage E im-- of the condenser in farads, E is the initialvoltage impressed on the condenser, and E1 is the reduced voltageimpressed on the condenser, the quantity of electricity discharged maybe expressed mathematically by the equation:

Obviously, if the voltage on a condenser is reduced to zero, thequantity of electricity discharged from the condenser is equal to theentire quantity of electricity stored on the condenser. Similarly, ifthe voltage impressed on the condenser is reduced from a higher to somelower value, the quantity of electricity discharged from the condenserwill be some fraction of the quantity stored on the condenser.

It will be further apparent that the polarity of the voltage-drop acrossthe resistor 32 in the discharge circuit of the condenser 24 is suchthat the change in voltage on the condenser 24 during the establishmentof its discharge circuit will be equal to the difierence between thevoltage to which the condenser 24 is charged Just prior to the instantthe discharge circuit is established and the voltage-drop across theresistor 32 while the discharge circuit is broken.

Now when it is considered that the current in the discharge circuitvaries with the rotational speed of commutator device 23 and that thevoltage-drop across the resistor 32 correspondingly varies with therotational speed of the commutator device 23, it will beseen that inaccordance with Equation 3, the variation of the voltage E1 therein,which is equivalent to the voltage-drop across resistor 32, will resultin a corresponding variation of the quantity Q of electricity dischargedfrom the condenser 24 each time the discharge circuit is established.Thus, since the voltage-drop across the resistor 32, that is E1, is lowat low speeds and high at high speeds, it will be seen that the quantityQ of electricity discharged from condenser 24 each time the dischargecircuit is established at a low speed will be greater than thatdischarged from the condenser 24 each time the discharge circuit isestablished at a high speed.

The current in the discharge circuit and consequently the voltage-dropacross the resistor 32 is thus not directly proportional to therotational speed of the vehicle wheel with which the commutator device23 is associated when the source, corresponding to the storage battery25, is of constant voltage. It will be apparent from Equation 3,however, that if the voltage of the source, which the battery 25represents, is made relatively high in comparison to the voltage-dropacross the resistor 32 at maximum vehicle speed, then the variation inthe quantity of electricity discharged from the condenser 24 each timethe discharge circuit is established at high and low speeds respectivelywill be a relatively low percentage. In such case, the current in thedischarge circuit, and consequently the voltagedrop across the resistor32, will approach closely to direct proportionality with the rotationalspeed of the commutator device.

The current in the discharge circuit may also be influenced somewhat bythe time constant of the discharge circuit so that at the high speeds ofvehicle travel it may be slightly less than would otherwise be the case.This efiect can. however, be minimized by providing a discharge circuithaving a low time constant.

The condenser unit 29 in the discharge circuit, being connected inparallel relation to the resistor 32 is charged to a voltagecorresponding'to the voltage-drop across the resistor 32 and stabilizesthe fluctuations in the pulsating directcurrent in the discharge circuitunder normal conditions of wheel deceleration.

The condenser unit 29 functions also upon a reduction of the voltageacross the resistor 32 occurring in response to deceleration of thewheels with which the commutator device 23 is associated to effect adischarge ofcurrent locally in the discharge circuit through theresistor 32 and the winding of the polarized relay 3|. The current sodischarged from condenser unit 29 will be equal to the product of thecapacitance of the condenser unit and the change in voltage to which itis charged, that is, the change in voltage across the resistor 32. Sincethe amount of the change in the voltage across the condenser unit 29occurring in a given time interval will vary in proportion to the rateof deceleration of from condenser unit 29 locally in the dischargecircuit through the .resistor 32 and the winding of relay 3| willcorrespond substantially to the rate of deceleration of the wheel unit.

The winding of the polarized relay 3| is so connected in the branchcircuit with the condenser unit 29 that the flow of current through thewinding thereof in a direction to charge the vehicle wheel unit, thecurrent discharged 76 the condenser 29 to the voltage across theresistor 32 when such voltage is increasing and the vehicle wheel unitcorrespondingly accelerating will be such as to bias the contact memberof the,

relay 3| to its open position. Conversely, when the voltage across theresistor 32 decreases, in. response to deceleration of the vehicle wheelunit,

the direction of flow of current discharged from the condenser unit 29through the winding of. the polarized relay 3| is reversed and causesoperation of the contact member of the relay to its closed position, ifthe current exceeds a certain value corresponding to a slipping rate ofdeceleration of the vehicle wheels. It the vehicle wheel unitdecelerates at a non-slipping rate,

the condenser. unit 29 likewise discharges current corresponding to thedeceleration rate through the winding of the polarized relay 3| but thecurrent is of insuflicient value to cause operation of the contactmember thereof to its closed position.

If the voltage-drop across the resistor 32 were directly proportional atall times to the speed of rotation of the wheel unit, the currentdischarged from the condenser unit 29 would always be the same for agiven rate of deceleration of the wheel unit regardless of whether thespeed of rotation of the wheel unit is high or low. However, aspreviously explained, the voltagedrop across the resistor 32 is notdirectly proportional to the rotational speed of the vehicle wheel unitand thus the rate of reduction of the voltage across the resistor 32 andthe voltage across the terminals of the condenser unit 29 will begreater at the lower speeds than at the higher speeds for a given rateof deceleration of the wheel unit. It will be apparent that this is sobecause, at the higher speeds, a greater change in speed must occur in agiven length of time, such as one second, in order to efiect the samereduction in voltage-drop across the resistor 32 and therefore the samereduction in voltage on condenser 29 as at the lower speeds.

It follows, therefore, that the contact member of the polarized relay 3|may be picked-up, for example, at a rate of rotative deceleration of thevehicle wheel unit of seven miles per hour per second at the lowerspeeds and at a rate of fifteen miles per hour per second at the higherspeeds. However, since a rate of rotative deceleration of the vehiclewheel of seven miles per hour per second is never attained unless thevehicle wheel is slipping, the fact that the contact member of thepolarized relay 3| will pick-up at different rates at the difi'erentspeeds is not a practical difilculty because in no case will it pick-upunless the wheel is slipping. At the higher speed, the pick-up of therelay 3| is slightly delayed compared to low speeds.

If, as previously stated, the voltage of the source corresponding to thebattery 25 is relatively high in comparison to the maximum voltage-dropacross the resistor 32 so that the voltage-drop across the resistor 32is almost directly proportional to the rotational speed of the vehiclewheel unit, then the percent variation in the rate of rotativedeceleration of the vehicle wheel unit eflective to cause pick-up of thecontact member of the relay ill at low speeds and at high speeds will beminimized, For example, the voltage of the source corresponding to thebatte y 25 may be such relative to the maximum voltage across theresistor 32 that the contact of the relay 8| will be operated to closedposition in response to a rotative deceleration of the Vehicle wheelunit at a rate exceeding ten miles per hour per second, at low spe dsand at a rate of rotative deceleration exceeding eleven miles per hourper second at high speeds.

Although the above-described apparatus is similar to the apparatusprovided in the above-men tioned Patent 2,270,413 of John Canetta, itshould be noted that the apparatus of the patent is effective solely fordetecting and registering the speed of rotation of a rotary element,such as a vehicle wheel, and is not efiective to register the rate ofchange of speed, such as the rate of rotative deceleration, of a rotaryelement or vehicle wheel as is the apparatus which we have disclosedherein.

As is well understood by those skilled in the art, a polarized relay isof such nature that, once the contact member thereof is actuated to agiven position in response to flow of current through the windingthereof in one direction, the contact member remains in such positionuntil the direction of flow of current through the winding of the relayis reversed and exceeds a certain value. Thus when a wheel unitbeglns'to slip, the contact member of the corresponding relay 3| isactuated to its closed position and remains in such position thereafteruntil the wheel unit begins to accelerate.

Each polarized relay 3| is arranged to control energization anddeenergization oi the magnet winding of the corresponding magnet valvedevice 2|.

The source of current for energizing the winding of each magnet valve 2|may be any suitable source of direct-current such as a storage battery5|. The separate source 5| is provided for this purpose, rather thanutilizing one of the sources 25, in order to avoid wide fluctuations inthe terminal voltage E of the sources 25.

The magnet valves 2| are identical and of wellknown construction and,accordingly, a brief description thereof is deemed suiflcient. Eachmagnet valve 2| comprises a suitable casing in which is contained adouble-beat valve 54 which is urged normally to an upper seated positionby a coil spring 55 and which is actuated to a lower seated position inresponse to energization 01' a magnet winding 56. In its upper seatedposition, the double-beat valve 54 is effective to establish com-.-munication through the branch pipe l8 of control pipe l5 to theassociated brake cylinder I3. In its lower seated position, thedouble-beat valve 54 closes the supply communication through the branchpipe l8 and establishes a communication through which fluid underpressure is exhausted from the brake cylinder |3 through an exhaust port51 at a rapid rate. v

Operation of equipment shown in Fig. 1 Let it be assumed that thevehicle having the equipment shown in Fig. 1 is traveling along thespondingly released. Since the vehicle is traveling at a constant speed,the contact member of each of the relays 3| is in the open positionthereor and consequently the magnet winding of the magnet valves 2| aredeenergized so that communication between the control pipe I 5 and brakecylindears I3 is open through the respective branch pipes It now theoperator desires to effect an application or the brakes he may do so,after first shutting-oil the propulsion power, by shifting the brakevalve handle Ila into the application zone an amount corresponding tothe desired degree of application of the brakes. The control pipe I! iscorrespondingly charged to a, pressure such as, for example, twenty-fivepounds per square inch corresponding to the degree of displacement tothe brake valve handle out of its brake release position and since themagnet windings of the magnet valve 2| are deenergized, fluid at acorrespondingpressure is supplied through the branch pipes It to thecorresponding brake cylinders l8 associated with the respective wheelunits. The brakes associated with the wheel units are accordinglyapplied in accordance with the degree of pressure established in thebrake cylinders. As long as the magnet windings or the magnet valves 2|remain deenergized the operator or the vehicle may vary the pressure inthe brake cylinder l3 and correspondingly the degree or application oithe brakes associated with the wheels by varying or shifting theposition of the brake valve handle.

Ii, during an application of the brakes or at the time that anapplication of the brakes is initiated, the wheels or a wheel unit beginto slip. further operation of the equipment occurs which will now bedescribed. Let it be assumed that the left-hand wheel unit begins toslip. In such case, the. contact member or the polarized relay 3|corresponding to such wheel unit is operated to its closed position toestablish the circuit for energizing the magnet winding of the magnetvalve zl associated with the corresponding brake cylinder 3. The circuitfor energizing the magnet winding of the magnet valve 2| is readilyapparent'irom the drawing and needs no description.

Upon energization of its magnet winding the magnet valve 2| is operatedto close communication through the branch pipe i8 to the correspondingbrake cylinder and cause fluid under pressure to be rapidly exhaustedfrom the brake cylinder. Accordingly, substantially at the instant thatthe wheels of .a wheel unit begin to slip, fluid under pressure israpidly vented from the corresponding brake cylinder i3 to cause acorresponding reduction inthe degree of application of the brakesassociated with the slipping wheel unit. As a result of the rapidreduction in the degree of application of the brakes associatedtherewith, the slipping wheels promptly cease to decelerate and begin toaccelerate back toward a speed corresponding to vehicle speed withoutdecelerating to a locked or non-rotative condition and sliding.

As previously stated, the contact member of the polarized relay 3|remains in its closed position, once it is actuated thereto, until thecurrent reverses in the operating winding of the relay. Thus, once thecircuit for energizing the magnet winding of the magnet valve 2| iscompleted, it

remains established until such time as the slipping wheels begin toaccelerate at a. rate exceeding a certain rate suiiicient to restore thereduce due to the supply of fluid under pressure to the vented brakecylinder l3. However, due

to the pressure maintaining feature of the brake. valve l1, previouslymentioned, fluid under pressure is automatically supplied to the controlpipe l to maintain a pressure therein corresponding to the position ofthe brake valve handle, notwithstanding the resupply of fluid underpressure to the brake cylinder it. Thus, if the operator of the vehicledoes not vary the position of the brake valve handle Ila, the fluidpressure restored in the brake cylinder It associated with the slippingwheel unit will be equivalent to the pressure established in the controlpipe I5.

If the pressure restored in the brake cylinder i3 is effective to causethe wheel unit to again begin to slip, the above operation is repeated.Thus at no time are the wheels permitted to attain a locked ornon-rotative condition and slide.

-If the operator of the vehicle operates the brake valve I! to reducethe degree of application of the brakes as the speed of the vehiclereduces, the fluid pressure reestablished in the brake cylinderassociated with the slipping wheels will be correspondingly reduced andthe likelihood of recurrence of wheel slipping lessened.

The contact member of the polarized relay 3| will ordinarily be restoredto itsopen position, in response to the acceleration of the slippingwheels, before the vehicle comes to a stop so that the magnet valve 2!will be correspondingly restored to its normal position. If it shouldhappen, however, that the contact member of the relay 3| remains in itsclosed position, at the time the vehicle comes to a stop, it willnevertheless be restored to its open position upon acceleration of thevehicle under propulsion power. Thus, the magnet valve 2| will always beproperly conditioned to provide open communication through the branchpipes l8 to the brake cylinders It at the time an application of thebrakes is initiated.

When a vehicle comes to a complete stop in response to an application ofthe brakes, the operator may vary the pressure in the brake cylinders 18as desired to secure any necessary degree of braking to hold the vehicleon a. grade. Before starting the vehicle again, the operator may releasethe brakes simply by restoring the brake valve handle Ila to its brakerelease position in which position the fluid under pressure in the brakecylinders i3 is vented to atmosphere along with the fluid under pressurein the control pipe [5 through the exhaust port [9 of the brake valve.

Equipment shown in Fig. 4

' diifers from that in Fig. i will accordingly be described.

The equipment shown in Fig. 4 differs from that in Fig. 1 with respectto the discharge circult associated with brush it of the commutatordevice 23. A transformer ll is provided having a primary windingconnected in the discharge circuit between the brush 2| and the groundconnection 48 and having the terminals of the secondary winding thereofconnected to the winding of a polarized relay Ila similar to the relayii. The contact member of the relay 3| a is arranged I to control thecircuit for energizing the magnet winding of the magnet valve 2i (notshown), as indicated in Fi .1.

A condenser Bil i connected in parallel relation with the primarywinding of the transformer 30 for the purpose of smoothing out-thefluctuating direct-current in the discharge circuit, which currentvaries substantially-in proportion to the rotational speed of the wheelsII, as in Fig. 1.

When the speed of rotation oi the wheels ll changes, the currentenergizing the primary winding of transformer 30 changes at acorresponding rate. The magnetic flux coupling the primary and secondarywindings of the transformer correspondingly reduces or increases at acorresponding rate and a voltage is thus induced in the secondarywinding of the transformer which is proportional to the rate of changeof current in the primary winding. Since the rate of change of currentin the primary winding is proportional substantially to the rate ofrotative deceleration or acceleration of the wheels, the voltage inducedin the secondary winding of the transformer will likewise besubstantially proportional to the rate of rotative deceleration oracceleration of the wheels. It will be apparent that the voltage inducedin the secondary winding is of one polarity when the wheels decelerateand of the opposite polarity when the wheels accelerate.

The. windings of the transformer 30 and the operating winding of thepolarized relay 3: are

. so designed and arranged that the voltage induced in the secondarywinding of the transformer will cause energization of the winding of therelay 3 la to a suflicient degree to cause operation of the contactmember thereof from its open to its closed position only in response tothe rotative deceleration of the wheels II at a rate exceeding a certainslipping rate. The operation of the contact member of the relay 3k: inresponse to slipping of the wheels efl'ectsoperation of the magnet valve2! associated therewith to cause fluid under pressure to be released ata rapid rate from the associated brake cylinder.

It will be understood that the normal fluctuations of the direct-currentin the primary winding of the transformer when the wheels are rotatingat a constant speed are eflective to produce an alternating current of acorresponding frequency in the secondary winding of the transformer. Thepurpose of the'condenser 6'0 is to prevent the variation of the currentin the primary winding at a sufficient rate normally that the voltageinduced in the secondary winding will cause pick-up of the relay "a. Thecapacitance of the condenser BI is insufficient to interfere with thereduction of current in the primary winding at a suflicient rate tocause pick-up of the relay 3m in response to slipping of the wheels IIIf the number of contact fingers ll on the commutator device 23 is largeso that the frequency of charge and discharge of the condenser dischargecircuit will then be less likely to pro-.

duce an undesired pick-up of the relay Ma. The condenser 60 may likewisebe omitted if the relay Sla is made to be slow-acting. If relay 3la isslow-acting it will respond to a continued rapid reduction of thecurrent in the discharge circuit occurring only when the wheels slip butnot to the normal fluctuating changes in current in the dischargecircuit during normal operation.

When the pressure of the fluid in the brake cylinder associated with theslipping wheels is reduced sufilciently, the wheels cease to decelerateand begin to accelerate back to a speed corresponding to car speed.Acceleration of the wheels causes an increase of the current in thedischarge circuit including the primary winding of the transformer 30and consequently a voltage of reverse polarity is induced in thesecondary winding. Such reversal of polarity of voltage induced in thesecondary winding of the transformer causes the contact member of therelay am to be restored to its open position interrupting the circuitfor energizing the magnet winding of the magnet valve M. The magnetvalve is accordingly restored to its normal position closing the exhaustcommunication from the brake cylinder and reestablishing the supplycommunication thereto.

In view of the complete description of the equipment shown in Fig. 1, itis believed unnec- The equipment shown in Fig. 1 is satisfactory for asingle rotary element or a limited number of rotary elements, such asthe wheels of a single car, but does not lend itself in a practicalmanner to a brake control equipment for a train of cars. It will beapparent that the provision of a separate storage battery for each wheelunit of train of cars would necessitate a large number of storagebatteries, the initial cost, as well as service and maintenance cost, ofwhich would present practical difllculties.

We have accordingly provided the brake control equipment shown in Fig. 5to illuistrate the application of our invention in a practical manner toa brake control equipment for a train of cars. The equipment shown inFig. 5 differs from that shown in Fig. 1 in providing a single voltagesource in the form of a generator I5 to act as the voltage source forall of the wheel units on a train of cars in place of a large number ofseparate batteries 25. Y

The generator 15 is adapted to be driven at a constant speed in themanner presently to be described and provides a voltage which, asdistinguished from the constant voltage of the batteries 25, varies withthe speed of travel of the train. As will be explained more fullyhereinafter, the generator 15 is a compound-wound generator of thedirect-current type having an overcompounded voltage characteristic sothat the terminal voltage of the generator varies in proportion to thetotal current supplied thereby to the separate commutator devices 23associated with the respective wheel units, which current in turn variesin accordance with the speed of 3! over a wide range of variation oftrain speed. It will be recalled that in the equipment shown in Fig. l,the relays 3! are not picked-up at exactly the same rate of rotativedeceleration of a corresponding wheel unit because the quantity Q ofelectricity discharged from the condenser 24 when the discharge circuitis established is higher at low speeds than it is at high speeds,-thereby causing variation in the voltage-drop across the resistor 32which is not directly proportional to the rotational speed of thewheels. By so designing the generator 15 that the increase in theterminal voltage of the generator under load conditions over the no-loadvoltage thereof is substantially equal to the voltage-drop across theresistor 32 at any given speed, it will be seen that the amount ofreduction in voltage impressed on the condenser 24 each time thedischarge circuit therefor is established will be a constant.

In other words if E represents the no-load voltage of the generator ande the increment of increase of terminal voltage of the generator underload conditions for a given voltage-drop e across resistor. 82, theamount of change D in voltage on the condenser 24 each time thedischarge circuit therefor is established may be expressedmathematically as follows:

(4) D= (E+e) -e=E That is, the amount of change of the voltage impressedon condenser 24 each time the discharge clrcuit therefor is establishedis a constant.

By reference to Equation 3, it will thus be seen that the quantity Q ofelectricity discharged from the condenser each time the dischargecircuit therefor is established will be substantially constant and,therefore, as previously explained, the current in the discharge circuitwill .be theoretically directly proportional at all times to therotational speed of the wheel unit.

In the case of a single rotary element, having a voltage source in theform of an over-compounded generator, the amount of the reduction in thevoltage-drop across the resistor 32 and that across the condenser unit29 effected in a given interval of time when the wheel unit isdecelerating will thus besubstantially constant for a given rate ofdeceleration. Accordingly, the current discharged from the condenserunit 29 locally in the discharge circuit'through the winding of therelay 3|, upon deceleration of the wheel unit will be substantially thesame for a given rate of deceleration regardless of whether the speed ofrotation of the wheel unit is high or low. In such case, therefore, therelay 3| in the discharge circuit will be picked-up at substantially thesame rate of rotative deceleration of the wheel unit whether the speedof rotation of the wheel unit is high or low.

In the equipment shown in Fig. 5, wherein the condensers 24 associatedwith a large number of wheel units are charged by the generator 15, theterminal voltage of the generator will vary in accordance with thecharging current which is in turn proportional to the speed of thetrain. Thus, if an individual wheel unit begins to slip, the voltage towhich the condenser 24 in the charging circuit of the correspondingwheel unit is charged is not reduced in accordance with the speed of theslipping wheel. The reduction in the voltage impressed on the condenser26 associated with a slipping wheel when the discharge circuit thereforis established accordingly increases somewhat with the reduction inspeed of the slipping wheel because of the greater reduction in thevoltage-drop across resistor 32 in comparison to the drop in voltage ofthe generator. The quantity of electricity discharged from suchcondenser 24, each time the discharge circuit therefor is established,accordingly does not remain exactly constant but increases slightly.However, since the voltage supplied by the generator 15 is adjustedinitially in accordance with the speed of the vehicle, the variationfrom a constant value of the quantity of electricity discharged from thecondenser each time the discharge circuit is established will be lessthan i the case of a constant voltage source.

It follows, therefore, that while the voltagedrop across the resistor 82associated with a slipping wheel is not exactly proportional to thespeed of rotation of the slipping wheel, it will be more nearly so thanin the case of a constant voltage source. Accordingly, the currentdischarged from the condenser unit 29 locally through the winding of therelay 3! upon the slipping of an individual wheel unit will be morenearly uniform for a given rate of deceleration than in the case of aconstant voltage source.

As previously indicated with respect to the embodimentshown in Fig. l,the current in the discharge circuit of each condenser 26 of theembodiment shown in Fig. 5 may tend to be somewhat reduced at highvehicle speeds due to the influence of the time constant of thedischarge circuit. This eifect can be approximately compensated for bythe proper over-compounding of generator 15.

Considering the equipment shown in Fig. 5 in detail, it will be seenthat the equipment shown is for a single railway car having twofour-wheel trucks located respectively at oppo site ends of the car,only one wheel of each wheel unit being shown.

The pneumatic apparatus whereby the operator controls the supply andrelease of fluid under pressure to and from the brake cylinders i3differs somewhat from that shown in Fig. l and will be brieflydescribed. As in Fig. 1, the main reservoir I6 is provided but thereservoir is located at the center of the car and is constantlyconnected to a train pipe, hereinafter called the supply pipe 6|. Abrake valve I! of the selflapping type is provided for controlling thepressure in a control pipe I5 just as in Fig. 1. The two pipes l5 and BIextend from end to end of the car and are provided with suitable hosecouplings 62 and angle cocks 63 in conventional manner whereby toconnect the sections of these pipes on successive cars. Connections areestablished between the brake valve l1 and the pipes I5 and GIrespectively by branch pipes 6d and 65 in which are interposed manuallyoperated valves 66. Valves 56 are turned to open position when it isdesired to control the pressure in the control pipe l5 from the brakevalve I! on the corresponding car. When it is desired to control thepressure in the control pipe l5 by a brake valve located on another car,not shown, the valves 66 in both branch pipes 64 and 65 are closed thusrendering the brake valve ii on the shown car non-operative.

Instead of providing an individual communication between each. brakecylinder and the control pipe i5 as in Fig. 1, the brake cylinders foreach truck are controlled by a relay valve device 58, of well-knownconstruction, which is in turn controlled according to the fluidpressure in control pipe supplied thereto through a branch pipe l8 ofpipe l5 under the control of a magnet valve 2|.

The relay valve 88 is of a super-sensitive high capacity type and isarranged to supply fluid under pressure from the supply pipe 6|, towhich it is connected by a branch pipe 69, to the brake cylinders it!through a brake cylinder pipe II in response to the operating fluidpressure supplied to the pressure chamber thereof through the branchpipe l8 from the control pipe 15. When the pressure in the control pipe15 is at atmospheric pressure the relay valve device 68 causes fluidunder pressure to be exhausted to atmosphere through an exhaust portthereof. When fluid under pressure is supplied from the control pipe l5to the pressure chamber of the relay valve device 68, the relay valvedevice operates to cause fluid under pressure to be supplied from thesupply pipe 6| to the brake cylinders l3 and establishes a pressuretherein corresponding to the pressure established in the control pipeIS.

A pressure operated switch I2, preferably of the snap-acting type, isconnected by a-branch ipe 13 to the control pipe [5 and is operativelycontrolled by the pressure therein. Any suitable type of pressureoperated switch may be provided. As diagrammatically shown, the pressureswitch 12 comprises a contact member a which is adapted to be snappedout of engagement with a pair of associated stationary contact memberswhen the pressure in the control pipe i 5 is reduced below a certain lowpressure, such as five pounds per square inch. When the pressure in thecontrol pipe increases above such pressure. the contact member a of thepressure switch 12 is snapped into contact with its associated pair ofcontact members. The function of thepressure switch I2 will be explainedhereinafter.

As in Fig. 1, each wheel unit of the equipment in Fig. 5 is providedwith an axle-driven commutator device 23 for alternately establishing acharging circuit for a condenser 24 and a discharge circuit including aresistor 32, a condenser unit 29, and a polarized relay 3!. Instead ofproviding a separate battery source, such as the storage battery 25, ineach condenser charging circuit for each wheel unit, the equipment shownin Fig. 5 provides a single source of direct-current potential, in theform of the compoundwound generator 15 previously mentioned, theterminal voltage of which is impressed on a pair of train wires I1 and18. The train wires 11 and 18 extend from end to end of the car and areprovided with suitable couplers 19 whereby the sections of the trainwires on successive cars may be connected.

The brush 2! associated with the commutator device 23 of each wheel unitis connected by a wire 45 to the train wire 11 which will hereinafter bereferred to as the positive traiii wire. The brush 26 associated withthe commutator device 23 of each wheel unit is connected by a wir 45 tothe train wire 18, the condenser 2| being interposed in the wire 46. Thetrain wire 18 will hereinafter be referred to as the negative trainwire.

The discharge circuit including the parallelconnected resistor 32 andseries-related condenser unit 29 and polarized relay 3| are connected ina circuit between the brush 28 associated with each commutator device 23of each wheel unit and the negative train wire 18.

The contact members of the two polarized relays 3I for each wheel truckare arranged in parallel relation so that the operation of either relay,effected in response to slipping of the corresponding wheel unit, mayestablish a circuit for energizing the magnet winding of the magnetvalve 2| for the corresponding truck.

The source of current for energizing the magnet windings of the magnetvalves 2! on each car is a storage battery 8| which is indicated asbeing the usual car lighting battery. As indicated by the legend in Fig.5, the storage battery 88 is adapted to be maintained fully charged by aIn order to supply a substantially constant battery voltage to the motor82, a voltage-regulator M, of suitable type, is provided. Thevoltage-regulator shown in Fig. 5 is of the type shown and described onpage 98 of the October 1923 issue of the Bell System Technical Journaland is accordingly not our invention.

Briefly, the voltage regulator M comprises a vacuum tube of the'threeelectrode type having a plate 81, grid 86 and filament 89.

The filament 89 is heated by current supplied from a suitable source,such as a battery 9i, and the current through the filament is controlledby a suitable rheostat 92.

The grid 88 is connected by a wire 93 to an intermediate point ofconnection between two resistors 9d and 95 the outer ends of which areconnected respectively to wires 98 and 9? connecting the motor 82 to thebattery 8|.

The plate 81 is connected by a wire 98 to the wire 96. A third resistor99 is interposed in the wire 96 bettween the respective points ofconnection thereto of the plate 87 and of the resistor 9%.

In operation, an increase of the battery voltage raises the gridpotential, thereby increasing the current through the tube and theresistor 89. Assuming the resistances of the resistors 95, 9d and 99 tobe 1'1, T2 and r3 respectively, and the mutual conductance of the tube86 to be y, it may be readily shown that by such choice of resistanceand tube that adapted to maintain a substantially constant voltagesupply over a wide range of variation of battery voltage. Thus,notwithstanding variations of the terminal voltage of the battery Bi,

the voltage impressed across the terminals of the motor 82 will remainsubstantially constant and the motor will therefore operate at asubstantially constant speed.

The motor 82 comprises a rotary armature winding 82a and a shunt fieldwinding 82f. As is well known, the shunt motor has a relatively fiat orconstant speed characteristic over a relatively wide range of loadcurrent.

The generator I5 comprises an armature winding "a, ashunt field winding15], and a series field winding 15s. As shown, the shunt field winding Iis connected directly across the brush terminals of the armature winding15a so that of the generator due to the fluctuating current supplied tocharge the condensers 24 associated with the different wheel units.Current is supplied from the output terminals of the generator 15 to thetrain wires i1 and 18 by branch wires I08 and I01 respectively. A doublepole knife switch its is provided for the purpose of interrupting theconnections between the output terminals of the generator is and thetrain wires i7 and it when desired.

In one of the branch wires, for example the wire SM, is interposed thepressure switch 12. Since the pressure switch 12 is operated to closedposition only upon an application of the brakes,

-it will be seen that when the vehicle is traveling along the road withthe brakes released, no current is supplied from the generator 75 to thecharging circuit associated with each wheel unit. Accordingly thegenerator '75 is driven at "noload when the vehicle is traveling alongthe road under power withthe brakes released. I

The relation and design of the field windings FM and 15s of thegenerator 15 are such as to obtain an over-compounded voltagecharacteristic so that the terminal voltage of generator is impressed ontrain wires 71' and i8 increases and decreases as the speed of the caror train increases and decreases, respectively.

It will be apparent that the current supplied to charge the condensers26 varies in direct proportion to the frequency of establishment of thecharging circuits therefor, and thus according to the speed of travel ofthe car or train. Accordingly since the load current of generator isflowing through the series field winding 75s varies with the speed oftravel of the car or train, the compounding of the generator may be sodesigned that the degree of increase in terminal voltage of thegenerator over the no-load voltage thereof will vary with the speed inunision with the variation in the voltage-drop across resistor 32 ineach of the discharge circuits, as previously pointed out in connectionwith Equation 4.

For reasons previously explained in connection with the equipment shownin Fig. 1, the voltage supplied by the generator is preferablyrelatively high compared to the voltage drop across resistors 32. Theno-load terminal voltage of generator 15 may, therefore, be of the orderof five hundred volts and the maximum voltage-drop across the resistors32 of the order of fifty volts.

When a plurality of cars are connected together in a train, only onemotor-generator equipment need be connected to the train wires I1 and18, the motor-generator equipments on other cars being out-out ofoperation by means of the knife switches 83 and I 08. It is desirable tohave only one motor-generator equipment in operation at one time becauseof the difficulty of operating a plurality of generators in parallelrelation. Obviously, in the case of modern high speed passenger trainsin which the cars and power-unit remain coupled and do not travel assingle cars, there is no need to provide a motorgenerator set on morethan one car. This one car may be and preferably is the power car.

It will be understood, therefore, that the greater the number of carsconnected together, the greater is the current load of the generator 15connected to the train wires 11 and 18. It is accordingly necessary tovary the degree of compounding of the generator 15 in accordance withthe number of cars in a train. To accomplish this, a diverter orresistor III is connected in shunt relation to the series field winding15s of the generator I and a movable contact arm H2 is shifted todifferent positions thereon in correspondence with the number of cars inthe train as indicated by the scale H3. It will be seen that with onlyone car in use, a maximum amount of the resistor ill is connected inparallel relation to series field winding He, thus diverting a minimumpercentage of current from the series field winding. As the number ofcars in the train increases, the contact arm 2 is positionedcorrespondingly to reduce the amount of the resistor III in parallelrelation to the series field winding s so that the percentage of currentdiverted from the series field winding 15s increases correspondinglywith the increase in the number of cars in the train. It will be seenthat by suitably adjusting th position of the contact arm H2 inaccordance with the number of cars in the train, at the time the trainis made up, a substantially uniform overcompounded voltagecharacteristic of the generator I5 relative to the speeds of the trainmay be obtained, notwithstanding variation in the number of cars in thetrain.

In view of the description of the equipment shown in Fig. 1, it isbelieved that the operation of the equipment shown in Fig. 5 will bereadily understood from the above description of the parts of the,equipment without any further specific description of the operation.

Summary Summarizing, it will be seen that we have disclosed severalembodiments of vehicle brake control apparatus including a novelelectrical device responsive to the rate 01' rotative deceleration of awheel or wheel unit of the vehicle for controlling the degree of thebrake application and particularly adapted to be responsive to the deceleration of an individual wheel or wheel unit of the vehicle at aslipping rate for efiecting a rapid release of the brakes associatedwith the slipping wheels to prevent the sliding thereof.

The electrical device responsive to the rate of rotative deceleration ofa vehicle wheel comprises a commutator or rotary switch device operatedin accordance with the rotational speed of the vehicle wheel foralternately charging a condenser to the voltage of a voltage-source anddischarging it into a discharge circuit at a frequency proportional tothe rotational speed of the vehicle wheel. Another condenser ofrelatively large capacity with respect to the first condenser isconnected in the discharge circuit in such a manner as to cause a localdischarge of current therefrom through the winding of a relaysubstantially in accordance with the rate of deceleration of the vehiclewheel. The relay is adapted to be picked up only in response to acurrent exceeding a certain value and corresponding to a certain rate ofrotative deceleration of the vehicle wheel unit occurring only when thewheel unit slips for effecting the rapid release of the brakesassociated with the vehicle wheel.

In one embodiment, the primary winding of a transformer is connected inthe discharge circuit associated with the commutator device While thesecondary winding of the transformer is connected to the operatingwinding of the relay. In this case, the reduction of the current in thedischarge circuit in accordance with the reduction in the speed of thevehicle unit at a slipping rate causes a sufllcient voltage to beinduced in the secondary winding of the transformer to cause pick-up ofthe relay and a consequent rapid release of the brakes.

In another embodiment, a single voltage source, in the form of anover-compounded generator driven at a constant speed, is providedinstead of a plurality of separate sources, such as storage batteries,for supplying current to charge the condensers associated with all theseparate wheel units of a car or train. Thus instead of charging thecondensers associated with the commutator devices to a constant voltageeach time the charging circuit therefor is established, the voltagevaries with the speed of travel of the car. This arrangement enables thepick-up operation of the relay for effecting the rapid release of thebrakes on a slipping wheel more nearly at the same slipping rate ofdeceleration, over a wide range of car speed, than the otherembodiments.

The last described embodiment is particularly adapted for operation inconnection with a train of cars. Since the current load on the generatorvaries with the number of cars, a diverter or resistor is connected inshunt relation to the series field winding of the generator and adjustedto different positions according to the number of cars in the train sothat notwithstanding the variation in the current load of the generatorin accordance with the number of cars, a substantially uniformover-compounded voltage characteristic relative to train speed isobtained.

It will be understood that the electrical apparatus responsive to therate of change of speed of a vehicle wheel or wheel unit may be employedin other situations than brake control equipment for registering therate of chang of speed of any rotary element. Accordingly, while we haveshown and described several embodiments of our invention particularly asembodied in connection with vehicle brake control equipment, it will beapparent that various omissions, additions, and modifications may bemade in the embodiments shown without departing from the spirit of ourinvention. It is accordingly not our intention to limit the scope of ourinvention except in accordance with the terms of the appended claims.

Having now described our invention, what we claim as new and desire tosecure by Letters Patent, is:

1. Apparatus for detecting the rate of rotative deceleration of a rotaryelement comprising, in combination, a source of direct-current voltage,an electrical condenser, a discharge circuit including a resistor and asecond electrical condenser in parallel with said resistor, meanseffective to cause the first said condenser to be alternately charged tothe voltage of said source and discharged into said discharge circuit ata frequency proportional to the rotational speed of the rotary elementto cause a direct-current to flow in the discharge circuit and to causethe said second condenser to be charged to a voltage corresponding tothe voltage-drop across said resistor and substantially proportional tothe rotational speed of the rotary element, said second condenser beingeffective to discharge current locally in the discharge circuit throughsaid resistor substantially proportional to the rate of reduction of thevoltage-drop across said resistor, and means responsive to a currentdischarged from said second condenser in the discharge circuit exceedinga certain value and corresponding to a certain rate of rotativedeceleration of the rotary element.

2. Apparatus for detecting the rate of rotative deceleration of a rotaryelement comprising, in combination, a source of direct-current voltage,an electrical condenser, a discharge circuit including aresistor and asecond electrical condenser in parallel relation with said resistor,means effective to cause the first said condenser to be alternatelycharged to the voltage of said source and discharged into said dischargecircuit at a frequency proportional to the rotational speed of therotary element to cause a directcurrent to flow in the discharge circuitsuch that the voltage to which the said second condenser is charged andcorresponding to the voltage-drop across said resistor is substantiallyproportional to the rotational speed of the rotary element, a polarizedrelay having an operating winding connected in series relation with thesaid second condenser in parallel with said resistor, the winding of thesaid relay being so connected that, upon an increase in the voltage-dropacross said resistor, the charging current of said second condenserflows through the winding in one direction and causes said relay to beoperated to a normal position and. upon a decrease in the voltage-dropacross said resistor. the current discharged from said second condenserflowsthrough the operating Winding of the relay in the oppositedirection and causes the relay to be actuated to an operative positiononly when the current discharged from the said second condenser exceedsa certain value corresponding to a certain rate of rotative decelerationof the rotary element.

3. Apparatus for detecting the rate of rotative deceleration of a rotaryelement comprising, in combination, a source of substantially constantdirect-current voltage, an electrical condenser, a discharge circuit forsaid condenser including a resistor and a second condenser in parallelrelation with said resistor, means effective to cause said firstcondenser to be alternately charged to the voltage of said source anddischarged into said discharge circuit at a frequency proportional tothe rotational speed of said rotary element to cause a flow ofdirect-current in the discharge circuit to produce a voltage-drop acrosssaid resistor varying substantially in proportion to the rotationalspeed of the rotary element and correspondingly charging said secondcondenser to said voltage, said second condenser being effective todischarge a current locally in the discharge circuit substantially inaccordance with the rate of reduction of the voltage-drop across saidresistor and therefore in accordance with the rate of rotativedeceleration of the rotary element, and current-responsive meansresponsive to a current so discharged from said second condenserexceeding a certain value and corresponding to rotative deceleration ofthe rotary element at a rate exceeding a certain rate.

4. Apparatus for detectingthe rate of change of speed of a rotaryelement comprising, in combination, an over-compounded generator of thedirect-current type, an electrical condenser, a discharge circuit forsaid condenser including a resistor, means eifective to cause saidcondenser sill to be alternately charged to the voltage delivered bysaid generator and discharged into said discharge circuit at a frequencyproportional to the rotational speed of said rotary element, saidgenerator supplying a voltage varying with the frequency of the chargingof said condenser so that a substantially constant quantity ofelectricity is discharged through the discharge circuit each time it isestablished thereby causing a flow of direct-current in the dischargecircuit which is substantially proportional to the rotational speed ofthe rotary element, and means responsive to the rate of change in thevoltagedrop across the resistor in the discharge circuit for registeringthe corresponding rate of change of rotational speed of the rotaryelement.

5. Apparatus for detecting the rate of change of speed of a rotaryelement comprising, in combination, an over-compounded generator of thedirect-current type, an electrical condenser, a discharge circuit forsaid condenser including a resistor, means effective to cause saidcondenser to be alternately charged to the voltage delivered by saidgenerator and discharged into said discharge circuit at a frequencyproportional to the rotational speed of said rotary element, saidgenerator supplying a voltage varying with the frequency of the chargingof said condenser so that a substantially constant quantity ofelectricity is discharged through the discharge circuit each time it isestablished thereby causing a flow of direct-current in the dischargecircuit which is substantially proportional to the rotational speed ofthe rotary element, and a second condenser connected in parallelrelation to said resistor in the discharge circuit adapted to be chargedto a voltage corresponding to the voltage-drop across said resistor andeffective upon a reduction of the voltage across said resistor todischarge current locally in said discharge circuit substantiallyproportional to the rate of reduction of the voltage across the resistorwhich is in turn substantially proportional to the rate of rotativedeceleration of said rotary element, and current-responsive meansoperatively responsive only to a current so discharged from said secondcondenser exceeding a certain value and corresponding to rotativedeceleration of the rotary element at a rate exceeding a certain rate.

6. Apparatus for detecting the rate of rotational deceleration of arotary element'comprising, in combination, a compound-wound generator ofthe direct-current type adapted to produce an over-compounded voltagecharacteristic, means for driving said generator at a substantiallyconstant speed, an electrical condenser, a discharge circuit for saidcondenser including a resistor and a second electrical condenser inparallel with said resistor, means effective to cause the first saidcondenser to be alternately charged to the volta e delivered by saidgenerator and discharged into said discharge circuit at a frequencyproportional to the rotational speed of the rotary element to cause adirect-current to fiow in the discharge circuit. said generator beingeffective to deliver a voltage which varies according to the currentsupplied thereby to charge the first said condenser substantially inunison with the variation in the voltage-drop across the resistor insaid discharge circuit, the quantity of electricity discharged from thefirst said condenser each time the discharge circuit is established.being substantially constant notwithstanding the variation'in speed ofrotation of the rotary element so that the direct-current in thedischarge circult is substantially proportional to the rotational speedof the rotary'element, said second condenser being effective upon areduction in the voltage across the resistor in the discharge circuitfor discharging current locally in the discharge circuit substantiallyproportional to the rate of reduction of the voltage across the resistorand accordingly substantially proportional to the rate of rotativedeceleration of the rotary element, and means responsive to the currentso discharged from said second condenser.

7. Apparatus for severally detecting the rate of change of speed of aplurality oi? separately rotatable rotary elements comprising, in combination, a compound-wound generator of the direct-current type havingan over-compounded.

voltage characteristic, an electrical condenser for each of said rotaryelements, a discharge circuit including a resistor for each of saidcondensers respectively, means for each rotary element eiiective tocause the corresponding condenser to be alternately charged to thevoltage delivered by said generator and discharged into .thecorresponding discharge circuit at a frequency proportional to therotational speed of the corresponding rotary element to cause adirectcurrent to flow in the discharge circuit, thevoltage-characteristic of said generator being such that the terminalvoltage under load conditions condenser is substantially proportional atall times to the rotational speed of the corresponding rotary element,and individual means for the discharge circuit of each condenserresponsive to the rate of change of current in the correspondingcircuit.

8. Apparatus for detecting the rate of rotational deceleration of arotary element comprising, in combination, a compound-wound generator ofthe direct-current type having an overcompounded voltage characteristic,8. motor for driving said generator having a substantiallyconstant-speed characteristic over a wide range of load variation for aconstant impressed voltage, a fluctuating source of voltage, avoltageregulator for causing a substantially constant voltage to beimpressed on the motor from said source, an electrical condenser, adischarge circuit for said condenser including a resistor, meanseifective to cause said condenser to be alternately charged to thevoltage delivered by said generator and discharged into said dischargecircuit at a frequency proportional to the rotational speed ofthe rotaryelement to cause a direct-current to flow in the discharge circuit,

current flowing, in the discharge circuit for each v said generatorbeing effective to deliver a voltage which varies according to thecurrent supplied thereby to charge said condenser and substantially inunison with the variation in the voltage-drop across the resistor insaid discharge circuit, the quantity of electricity discharged from saidcondenser each time the discharge circuit therefor is established beingthus substantially constant notwithstanding the variation in speed ofrotation of the rotary element so that the direct-current in thedischarge circuit is substantially proportional to the rotational speedof the rotary element, and means operatively responsive to the rate ofchange of voltage across the resistor in said discharge circuit.

9. Apparatus for severally detecting the rate of change of speed of aplurality of separately rotatable rotary elements comprising, incombination, a compound generator of the direct-current type driven at asubstantially constant speed, said generator having a series fieldwinding and a shunt field winding so designed and constructed that thegenerator has an over-compounded voltage-characteristic variableaccording to the variation of current energizing the series fieldwinding, an electrical condenser for each of said rotary elements, adischarge circuit including a resistor for each of said condensersrespectively, individual means associated with each rotary elementrespectively effective cause the corresponding condenser to be alternately charged to the voltage delivered by said generator and dischargedinto the corresponding discharge circuit at a frequency proportional tothe rotational speed of the corresponding rotary element to cause adirect-current to flow in the corresponding discharge circuit, meansassociated with the series field winding of said generator for socontrolling the amount 01 current therethrough in proportion to thenumber of condensers charged by said generator as to cause the generatorto produce a substantially uni- I form over-compoundedvoltage-characteristic relative to the rotational speed of said rotaryelements whatever the number of condensers amount corresponding to thevoltage-drop across ,3

the resistor of the discharge circuit of each rotary element, eachcondenser being effective cor-

